The GCOM-C1 program was approved by Japanese Space Activity Commission in December, 2009.

• The system design and EM design of GCOM-C1 including SGLI started in July 2009

• The SGLI PDR was over in March, 2010. The manufacturing of SGLI EM has been started.

• The CDR (Critical Design Review) of GCOM-C1 satellite system was held in Feb. 2013, and JAXA has started manufacturing the flight model components of GCOM-C1 satellite. 1)

In July 2017, the GCOM-C project received the nickname Shikisai (meaning colors in Japanese). The nickname was chosen by JAXA in a public contest. 2)

The purpose of the GCOM project is the global, long-term observation of the Earth's environment. GCOM is expected to play an important role in monitoring both global water circulation and climate change, and examining the health of Earth from space. 3)

H-IIA launch vehicle No. 37 incorporates JAXA's newly developed technology to insert GCOM-C1/Shikisai and SLATS/Tsubame into different orbital altitudes, respectively. It will expand opportunities of multiple satellite launch and take full advantage of the capability of H-IIA.

Real-time observation data over Japan are transmitted by X-band to JAXA's ground stations at Katsuura, or EOC (Earth Observation Center at Hatoyama, Saitama). The received data are distributed immediately after Level-1 data processing.

Global observation data observed by SGLI are transmitted in X-band to KSAT (Kongsberg Satellite Services) Station in Svalbard, Norway together with some HK data. KSAT is the commercial Norwegian company. GCOM-C1 transmits telemetry stored in the onboard recorder at relatively fast data rate of 1Mbit/s to KSAT/Svalbard by S-band/QPSK..

Secondary payload:

• SLATS/Tsubame, a minisatellite of JAXA with a launch mass of 400 kg.

- The launch vehicle will insert the SLATS/Tsubame minisatellite into a lower orbit of ~ 500 km.

• January 12, 2018: JAXA has released some sample observation first-light images of Earth acquired with the GCOM-C/Shikisai mission. Evergreen forests are seen in dark green in the true color image and cannot be discriminated, while in the false color image, evergreen forests are clearly visible in bright green colors (Figure 4). On the other hand, small yellow patches are seen in the enlarged false color image in the lower right of Figure 4. These are golf courses covered with faded grasses on winter. 8)9)

Figure 4: Left: A true color composite image (reflectances of SGLI VN8, VN5, VN3 channels are assigned to red, green, and blue colors); Center: A false color composite image (reflectances of SGLI VN8, VN11, VN3 channels are assigned to red, green, and blue colors). The images have a resolution of 250 m and were captured over the Kanto area in Japan with SGLI around 10:30 JST on 6 January 2018. Lower Right: detail enlarged composite image (image credit: JAXA/EORC)

Figure 5: Left: The image is a true color composite (reflectances of SGLI VN8, VN5, VN3 channels are assigned to red, green, and blue colors);Middle: A near-ultraviolet (NUV) image; Right: Degree of polarization (POL) image. The images were captured over the Ganges river, India with SGLI onboard the SHIKISAI around 11:40 (JST) on 03 January 2018. Dense aerosols are seen around the mouth of Ganges river to coastal ocean in the NUV image. In the DPOL image, the solar light reflected at the ocean surface is seen to be highly polarized. SGLI can observe aerosols over land and ocean using the functions of NUV and polarization observations (image credit: JAXA/EORC)

Figure 6: These images are color composite (reflectances of SGLI VN7, VN6, VN4 channels are assigned to red, green, and blue colors) images around the Island of Tsushima (middle) and around the Kanto area (right) observed with SGLI onboard the SHIKISAI around 11:10 (JST) on 01 January 2018. The locations of the images are shown in the left image. SGLI can observe the spatial distribution of ocean colors with the spectral channels of high sensitivity designed for ocean color observation in order to retrieve the concentrations of suspended matter and phytoplankton in water. These observations are useful for fishery prediction and the monitoring of red tide occurrence (image credit: JAXA/EORC)

Figure 7: This image is a true color composite (reflectances of SGLI VN8, VN5, VN3 channels are assigned to red, green, and blue colors) image of 250 m spatial resolution captured over the Okhotsuk Sea and Japan Islands with SGLI onboard the SHIKISAI around 10:20 (JST) on 6 January 2018. Snow, sea ice, and clouds are shown in white. Land and ocean areas are seen in dark brown and blue colors (image credit: JAXA/EORC)

Figure 8: This image is a false color composite (reflectances of SGLI SW3, VN11, VN8 channels are assigned to red, green, and blue colors) image of 250 m spatial resolution captured over the Okhotsk Sea and Japan islands with SGLI onboard the SHIKISAI around 10:20 (JST) on 6 January 2018. Snow and sea ice are shown in deep blue while water and ice clouds are seen in white and light blue, respectively. Sea ice are formed along the eastern coast of the Eurasia Continents and spreads along the east side of Sakhalin flowing down to the south (image credit: JAXA/EORC)

- The project will continue the initial functional verification (for about three months after launch,) then confirm data accuracy by comparing it with observation data acquired on land, and perform initial calibration and inspection operations including data correction.

• December 24, 2017: JAXA received telemetry data from GCOM-C1 /SHIKISAI and SLATS/TSUBAME, confirming that their satellite attitude control system had transitioned to the steady state. The current status of both satellites is stable. 10)

- Subsequently, the following procedure occurred – power generation that supports the satellites' operation by the deployed solar array wings, ground communications and sound attitude control that maintains those operations. Combined by the completion of the series of other operations, such as powering up of the bus and mission equipment, the satellites have entered the state where they can be sustained in orbit. This concludes their critical operations phase.

- SHIKISAI and TSUBAME will move on to the next operations phase, where the functions of the satellites' onboard apparatus will be examined approximately in the next three-month period.

- JAXA conveys deep appreciation for the support by all for the satellites' launch and tracking.

SGLI is an advanced multi-purpose visible/infrared (VNIR, SWIR, TIR) imager of GLI heritage, flown on ADEOS-II. The objective is to measure ocean color, SST (Sea Surface Temperature), land use and vegetation, snow and ice, clouds, aerosols and water vapor, etc. 12)13)

• The prime goal of SGLI is to retrieve global aerosol distributions. To achieve this target, SGLI will have 2 polarization channels with 3 directions

• SGLI is mainly focused to land and coastal areas. There are 11 channels with an IFOV of 250 m. GLI on ADEOS-II had only 6 channels of 250 m resolution.

The SGLI assembly features two separate sensors (radiometers) labeled VNIR (Visible Near Infrared) and IRS (Infrared Scanner). Note, the VNIR device is also referred to as VNR in the text.

• VNIR is a pushbroom instrument providing 14 channels in the VNIR spectral region (actually also in the UV), 11 channels are termed VNIR-NP (VNIR Non-Polarized), and 2 channels are called VNIR-P (VNIR-Polarized). The VNIR-P channels of the polarimeter provide 3 polarization angles at: 0º, 60º, and 120º.

The VNIR-NP channels are divided into three 24º pushbroom type telescopes configured in the cross-track direction to realize the wide FOV (70º) requirement with wide spectral range (380 nm to 865 nm). Each telescope has refractive telecentric optics and 11 channels CCD on which the '11 channel bandpass filter assembly' is mounted. 14)

To realize the VNIR-P polarization observation, three linear polarization channels (0º, 60º and 120º) are set for two pushbroom telescopes which are dedicated for 670 nm and 865 nm observation. A tilting operation around the Y-axis of ±45º is required for VNIR-P to observe aerosols (scattering angle requirement). The scattering angle observation is calculated using the satellite orbital position, sun and observation target direction. A scattering angle direction between 60º and 120º is required for the aerosol retrieval over the land surface.

SGLI has a capability of simultaneous nadir and slant observations. In addition, the sensor has a capability of along-track multiangle observation. A chance of multi-angle observations on forest areas with less cloud influence will increase comparisons with cross- track observations. In the GCOM –C1 project, global AGB (Above Ground Biomass) data will be provided as a standard product that is estimated by taking advantage of the multiangle observation capability.

The key VNIR observation channels such as 670 nm and 865 nm are being observed with both low and high dynamic range independently according to the requirements (Table 2). The total spectral channels for SGLI are optimized to 19 channels including tilting polarization observation (there were 36 channels for GLI instrument). On the other hand, the SGLI standard products are increased from 22 products of GLI to 29 products.

The basic IFOV (Instantaneous Field of View) is set to 250 m - compared to GLI's 1 km requirement. Using this higher resolution with a wide FOV (1150 km for VNR and 1400 km for IRS), it is expected that the human activity influence on Earth's environment can be studied.

The optical SGLI instrument is being designed and developed at NEC Toshiba Space, Tokyo, Japan. In turn, NEC Toshiba Space selected Sofradir of France to provide the infrared detectors for SGLI. As of 2008, Sofradir is providing concept studies for the cooled infrared MCT (HgCdTe)focal plane array detectors of the SGLI instrument. The two TIR arrays are centered on 10.8 and 12 µm wavelengths respectively, which are hybridized on a single readout circuit for accurate registration. 15)16)17)

The IRS whiskbroom scanner features six channels in the region of 1.05 µm to 12 µm (Table 3). The 45º tilted scan mirror is rotated around the X-axis continuously to realize a scan of 80º for Earth observation; in addition, the onboard calibrator (blackbody, solar diffuser, and inner light source) and deep space are being scanned on each scanner revolution. Compared with the double-sided mirror employed on GLI and MODIS, the constant incident angle to the IRS scan mirror represents an advantage for the calibration function.

The observation light is directly focused onto the focal plane using a Ritchey-Chretien type telescope without any relay optics. The infrared spectral range is divided by the dichroic filter for the SWIR and TIR regions in order to optimize the detection process.

The four SWIR channels employ an InGaAs photodiode detector array cooled to -30ºC using a Peltier thermo electronic cooler. The two TIR channels use a photovoltaic type HgCdTe (PV-MCT) detector array cooled to 55 K by a Stirling-cycle cooler. The bandpass filters corresponding to the spectral channels are mounted on the focal plane in the detector packages.

The solar diffuser (made of Spectralon), the inner light source using LEDs (Light Emitting Diodes) for the SWIR channels and a high-emissivity blackbody for the TIR channels, are used as the onboard calibrator. These calibration sources and a deep space window, arranged around the scan mirror, make it possible to obtain calibration data on every scan.

Region covered

Geophysical products

Resolution

Land

Precise geometrically corrected image

250 m

Atmospherically corrected land surface reflectance

250 m

Vegetation index including NDVI and EVI

250 m

Vegetation roughness index including BSI_P and BSI_V

1 km

Shadow index

1 km

Land surface temperature

500 m

Fraction of absorbed photosynthetically active radiation

250 m

Leaf area index

250 m

Above ground biomass

1 km

Land net primary production

1 km

Plant water stress trend index

500 m

Fire detection index

500 m

Land cover type

250 m

Land surface albedo

1 km

Atmosphere

Cloud flag including cloud classification and phase

Scene: 1 km
Global: 0.1º

Classified cloud fraction

Cloud top temperature and height

Water cloud optical thickness and effective radius

Ice cloud optical thickness

Water cloud geometrical thickness

Aerosol over ocean by visible and NIR (Near Infrared)

Aerosol over land by NUV (Near Ultraviolet)

Aerosol over land by polarization

Long -wave radiation flux

Short-wave radiation flux

Ocean

Normalized water leaving radiance

Coast: 250 m
Open ocean: 1 km
Global 4-9 km

Atmospheric correction parameters

Ocean photosynthetically available radiation

Euphotic zone depth

Chlorophyll-A concentration

Suspended solid concentration

Absorption coefficient of colored dissolved organic matter

Inherent optical properties

SST (Sea Surface Temperature)

Coast: 500 m, other: ditto

Ocean net primary production

Coast: 500 m, other: ditto

Phytoplankton function type

Coast: 250 m, other: ditto

Red tide

Multi sensor merged ocean color parameters

Coast: 250 m, open ocean: 1 km

Multi sensor merged SST (Sea Surface Temperature)

Coast: 500 m, open ocean: 1 km

Cryosphere

Snow and ice covered area

Scene: 250 m, global: 1 km

Okhotsk sea-ice distribution (Note: Okhotsk is a sea lying between the
Kamchatka Peninsula on the east, the Kuril Islands on the southeast,
the island of Hokkaidō to the far south, the island of Sakhalin along
the west, and a long stretch of the eastern Siberian coast)

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).